Supporting element of adjustable length

ABSTRACT

A normally upright, telescopically adjustable, supporting element, such as a leg for a stool, has a cylinder whose cavity is axially divided into two chambers by a partition. The lower chamber is liquid-filled, the upper chamber contains liquid under the pressure of a gas cushion, and the two chambers may be connected by a valve in the partition. The position of a plunger axially projecting from the lower chamber is generally determined by the amount of non-compressible liquid in the lower chamber, but limited axial movement is made possible by a gas cell partly bounded by the plunger and otherwise by a sealing member separating the gas in the cell from the liquid in the lower chamber.

United States Patent 91 Freitag 1 SUPPORTING ELEMENT OF ADJUSTABLELENGTH [75] Inventor: Herbert Freitag, Koblenz-Lutzel,

Germany [73] Assignee: Stabilus lndustrie und Handelsgesellschatt MBl-l,Koblenz-Neuendorf, Germany [22] Filed: Apr. 3, 1972 [21] Appl. No.:240,646

[58] Field of Search 248/399, 400, 404, 188.2, 248/188.8, 188.3, 354 H;297/347; 188/314, 322

[56] References Cited UNITED STATES PATENTS 2,042,443 5/1936 Buckstone248/404 3,142,156 7/1964 Mills et a1 248/354 l-l 3,163,262 12/1964Allinquant 188/314 3,388,883 6/1968 Axthamrner et a1. 248/l88.2

[11] 3,787,019 1451 Jan.22, 1974 3,656,593 4/1972 Bauer 248/354 HFORElGN PATENTS OR APPLlCATlONS Primary ExaminerMarion Parsons, J r.

[57] ABSTRACT A normally upright, telescopically adjustable, supportingelement, such as a leg for a stool, has a cylinder whose cavity isaxially divided into two chambers by a partition. The lower chamber isliquid-filled, the upper chamber contains liquid under the pressure of agas cushion, and the two chambers may be connected by a valve in thepartition. The position of a plunger axially projecting from the lowerchamber is generally determined by the amount of non-compressible liquidin the lower chamber, but limited axial movement is made possible by agas cell partly bounded by the plunger and otherwise by a sealing memberseparating the gas in the cell from the liquid in the lower chamber.

10 Claims, 3 Drawing Figures PATENTED JAN 2 2 I974 SHEET 2 0F 2 Thisinvention relates to telescopically adjustable supporting elements, andparticularly to improvements in a supporting element whose principalelements are a cylinder partly filled with liquid and a plunger axiallyprojecting from the cylinder.

It is known to provide the cylinder of such an element with two chambersof which one is filled with liquid and receives an axially terminalportion of the plunger whereas the other contains a reserve of liquid.When it is desired to change the effective length of the supportingelement, liquid is transferred between the chambers to expel or toretract the plunger. Because the liquid is practically incompressible, asupporting element of the type described is rigid in an axial directionunless a cushion of compressed gas is provided in pressure transmittingrelationship with the liquid receiving the plunger. Such a knownmodification of the basic supporting element makes the construction ofthe element rather complex and costly, and makes it very difficult toset the element to a desired precise length.

A basic object of this invention is the provision of a supportingelement of variable length which resiliently resists axial stress with aforce independent of the effective length of the element, and thuspermits the length of the element under a fixed load to be set withgreat precision prior to loading.

Another object is the provision of such a resilient support which is ofsimple and rugged construction and thus capable of long, reliableservice while permitting manufacture at low cost.

With these and other objects in view, as will hereinafter becomeapparent, the invention provides a supporting element in which thecavity of a cylinder is axially divided into two chambers by a fixedpartition. A valve operatively interposed between'the chambers may bemoved between an open position and a closed position by an operatingmechanism accessible outside the cylinder cavity.

A first one of the chambers contains an amount of gas undersuper-atmospheric pressure and a first body of liquid inpressure-transmitting relationship. A plunger is axially movable in thecylinder and has respective terminal portions in the second chamber andoutside the cylinder. Yieldably resilient means bias the plunger outwardof the cylinder. Although a second body of liquid fills the remainder ofthe second chamber and communicates with the first body only in the openposition of the valve, the yieldably resilient means permit limitedmovement of the plunger inward of the second chamber when the valve isin its closed position.

Additional features of this invention and many of the attendantadvantages thereof will readily be appreciated as the same becomesbetter understood from the following detailed description of preferredembodiments when considered in connection with the appended drawing inwhich:

FlG. 1 shows an adjustable stool leg of the invention in fragmentaryelevational section; and

FlGS. 2 and 3 show modifications of the device of FIG. 1 in respectivecorresponding views.

Referring now to the drawing in detail, and initially to FIG. 1, thereis seen the single, adjustable leg of a stool, not otherwise shown. Anupper portion of the leg is formed essentially by a tubular sheet-metalcylinder 12, and the lower portion by a plunger 1 coaxially projectingfrom the radial bottom wall 2 of the cylinder. The plunger 1 movablyenters the cylinder through a central opening of the bottom wall 2 inwhich it is sealed by an annular packing 3 held in position by acylindrical spacer 4. The spacer 4 is axially secured by an internal,annular shoulder on the cylinder 12 corresponding to a groove 4a rolledinto the outer cylinder face.

The radial top wall of the cylinder 12 is formed by a fixed plug 114projecting outward of the cylinder and externally threaded over much ofits projecting length for assembly with the seat of thestool by means ofa suitable connector, not shown. A rod 13 passes axially through acentral bore in the plug 14 and carries a seal ing ring 23 in the bore.A transverse bar 13a permits the end portion of the rod 13,accessibleoutside the cavity of the cylinder 12, to be moved axially.

. The cylinder cavity is divided axially into an upper chamber and alower chamber by a partition 10 held in a fixed axial position betweentwo internal shoulders of the cylinder wall corresponding to rolled,circumferential grooves 18 on the outer cylinder face. The partition 10is sealed to the cylinder 12 by a ring 19. A central bore in thepartition 10 receives the lower end portion of the rod 13 with ampleclearance, but a resilient ring 20 partly retained in a circumferentialgroove of the rod forms a valve which closes the conduit in thepartition 10 when in the illustrated position and seals the two chambersof the cylinder cavity from each other.

Outward movement of the rod13 from the illustrated position inthecylinder 12 is prevented by a washer 21 on the free inner end of therod which abuttingly engages the lower radial face of the partition 10.When the rod 13 is pushed inward of the cylinder cavity, the valve ring20 enter the lower cylinder chamber and permits fluid to flow throughthe annular conduit around the rod 13 in the bore of the partition 10.The upper chamber holds a body of liquid 1 1 whose free, horizon talsurface is in direct pressure-transmitting contact with an amount of agas 22 under a pressure higher than atmospheric pressure. The gas fillsthe remainder of the first chamber.

The lower cylinder chamber is provided with a piston 8 which is axiallymovable and divides the chamber into two compartments 5, 9 communicatingthrough throttling passages 15 in the piston 8 and as completely filledwith another body of liquid as is possible. Any gas that may be presentinitially in the lower cylinder chamber ultimately makes its way to thegas 22 in the upper chamber.

The piston 8 is axially fastened on the tubular upper end of the plunger11 between two integral shoulders of the latter. The cylindrical, blindbore of the plunger 1 is sealed from the liquid in the upper compartment9 of the lower cylinder chamber by a cylindrical plug 7 carrying aresilient sealing ring 17 to retain a body of highly compressed gas inthe cell 6 axially bounded in the plunger bore by the plug '7 and theclosed end of the bore. The plug 7 is normally held by the gas in thecell 6 against a spring washer 16 which prevents ejection of the plugfrom the plunger 1.

As long as the resilient valve ring 20 is in the illustrated position,the length of the illustrated support element when free from an appliedload is precisely determined by the combined amount of incompressibleliquid in the compartments 5,9. The plug 7 abuts against the washer l6,and the plunger 1 cannot be pulled outward of the cylinder by a forcenot capable of causing cavitation in the liquid below the partition 10..

When an axial load is applied to the support element, pressure istransmitted from the plunger 1 to the liquid in the compartments 5', 9,the plug 7, and the compressed gas in the cell 6. The plunger 1 can moveinward of the cylinder 12 to the extent that the applied force can drivethe plug 7 inward of the cell 6 and further stress the gas whosereaction to a load of known magnitude is precisely predictable, and maybe chosen by selecting the dimensions of the apparatus and the pressureof the gas. The stress in the gas is partly relaxed during outwardmovement of the plunger 1, and such relaxation is limited by abuttingengagement of the plug 7 by the washer 16. The resiliency of the supportelement is entirely independent of its effective length and the amountof liquid in the compartments 5, 9. i

The latter amount controls the overall length of the element. if thislength is to be changed, the valve ring 20 is moved to its open positionby means of its operating rod 13, and liquid is permitted to flowdownward through the partition 10 under the pressure of the gas 22, oris forced to flow upward through the partition under a compressive,external force applied to the cylinder 12 and the plunger 1. Too suddena length change is prevented by the reduced flow section of thethrottling passages 15. The piston 8 also guides the plunger 1 and theplug 7 on the plunger during their joint axial movement. The valve ringis returned manually to the illustrated, closed position as soon as theelement has reached the desired increased or decreased length.

The pressures of the gas 22 in the first cylinder chamher and of the gasin the cell 6 are chosen so that the plug 7 remains in the illustratedposition of abutment against the spring washer 16 when the valve ring 20is in its open position, that is, the force exerted by the gas in thecell 6 on the plunger 1 and tending to shift the plunger outward of thecylinder 12 must always be greater than the corresponding force of thegas 22 transmitted to the plunger by-the liqud ll. Under theseconditions, the volume of the cell 6 remains constant at its maximumvalue while the valve in the partition 10 is open during adjustment ofelement length, and the adjusted length is not changed after closing ofthe valve by volume changes of the cell 6.

The modified stool leg shown in H6. 2 is identical with that describedabove in detail with reference to FIG. 1 except as specifically statedhereinbelow.

The plunger 1 is a solid piece of metal of circular cross section. itpasses through an annular bottom wall 2 provided with inner and outersealing rings 3a, 3b. The piston 8' slidably engages the wall of thecylinder 12 and also the plunger 1' and is provided with inner and outersealing rings 25, 26, and with throttling passages 15. A container 24having-the shape of an inverted cup is fixedly fastened to the piston 8'in a manner not explicitly shown, and its rim is in fluid-tightengagement with the radial top face of the piston. The upper terminalportion of the plunger 1 passes movably through the central opening ofthe piston 8' into a cell 6 within the container 24, filled with a gasunder high pressure as described above. A coaxial split ring 29 partlyreceived in a groove of the plunger 1' abuts against a shock absorbingring 27 on the piston 8' in the illustrated relative position of pistonand plunger, and a shock absorbing pad 28 on the bottom of the cupshapedcontainer 24 in the cell 6' reduces noise when the plunger 1' moves tothe non-illustrated terminal position of its stroke relative to thecontainer 24.

The valve operating rod 13 differs from the aforedescribed rod 13 bybeng provided with an annular abutment 35 limiting movement of the rodinward of the cylinder 12, and by being sealed to the fixed, threadedplug 14' constituting the radial top wall of the cylinder by a packing23a recessed in the plug 14' and movably engaging the smooth cylindricalsurface of the rod 13'. r

Under normal operating conditions, when the conduit in the partition 10is blocked, a load axially applied to the supporting element andsufficient to overcome the resistance of the compressed gas in the cell6 can shift the plunger 1' inward of the cylinder 12, and the plungermoves outward again when the load is reduced or removed. The illustratedelement thus permits an attached seat to yield resiliently when theweight of an occupant is shifted as is conventional in spring mountedseats. The cell 6' provides a pneumatic spring whose characteristics areentirely independent of the amount of liquid in the lower cylindercompartment and of the effective length of the supporting element.

When the valve ring 20 is moved into its open position in thecompartment 9 by means of the rod 13, and no load is applied to thesupporting element, the plunger 1' is moved outward of the cylinder 12through the bottom wall 2', and shifts the piston 3' and container 24downward. The rate of this movement is slowed by the flowresistanceencountered by the liquid passing upward from the compartment5 to the compartment 9 through the throttling passages 15 in the piston8. The pressure of' the gas in the cell 6' exerts a sufficiently greateraxial force on the plunger 1 than the gas 22 that the relative positionof the plunger and the piston 8' is not changed while the valve ring 20is in its open position. When the ring is returned to the illustratedclosed position, the length of the supporting element does not changefurther unless a load is applied. I

When it is desired to shorten the element, the conduit in the partition10 is opened, and the plunger 1' is pushed inward of the cylinder 12 ata rate controlled by the resistance of the passages 15 to downward flowof liquid. The gas 22 is compressed to admit additional liquid to theupper chamber Of the cylinder 12, but no significant displacement of theplunger 1' relative to the container 24 can occur, and the unloadedlength of the element after the closing of the valve in the partition 16is the same as the length was at the moment of valve closing under anapplied load.

The supporting element illustrated in H6. 3 is identical with thatdescribed with reference to FIG. 2 except for the devices in the upperend of the cylinder 12. The partition 10' and the externally threadedplug 14", not significantly different from the partition it) and theplug 14, are integrally connected by a coaxial tube 30. Several radialbores 31 in the tube 30 adjacent the partition 10' connect the portionof the upper cylinder chamber filled with liquid ill to an annularchamber 33 about a reduced portion 34 of the valve operating rod 13". inthe illustrated position of the rod, the chamber is axially bounded byconically flaring parts 32, 32a of the rod and sealed by resilient rings23, 2% closely adjacent the conical parts, the ring acting as a valvewhich, in the illustrated position, blocks the flow of liquid betweenthe two cylinder chambers through the bores 31, only one being seen inthe drawing, and the annular chamber 33.

The apparatus shown in FIG. 3 operates in the same manner as describedabove with reference to FIG. 2.

It should be understood, of course, that the foregoing disclosurerelates only to preferred embodiments of the invention and that it isintended to cover all changes and modifications of the examples of theinvention herein chosen for the purpose of the disclosure which do notconstitute departures from the spirit and scope of the invention as setforth in the appended claims.

What is claimed is:

1. A supporting element of adjustable length comprising, in combination:

a. a cylinder member having an axis and defining a sealed cavitytherein;

b. a partition fixed to said cylinder member in said cavity and axiallydividing the cavity into a first chamber and a second chamber;

0. valve means operatively interposed between said chambers and movablebetween respective open and closed positions in which said valve meansconnects said chambers and seals said chambers from each other;

d. valve operating means accessible outside said cavity for moving saidvalve means between said positions thereof;

. a first body of liquid in said first chamber;

f. an amount of a gas under a pressure higher than atmospheric pressurein pressure-transmitting relationship to said body of liquid;

g. a plunger member axially movable in said cylinder member,

1. said plunger member having respective axially terminal portions insaid second chamber and outside said cylinder;

h. a second body of liquid substantially completely filling theremainder of said second chamber and communicating with said first bodyin said open position of the valve means,

1. whereby said gas in the open position of the valve means exerts afirst axial force on said plunger member in a direction outward of saidcavity when said valve means is in the open position thereof; and

. yieldably resilient means in said second chamber opposing movement ofsaid plunger member inward of said second chamber with a second forcesubstantially greater than said first force when said valve means is inthe closed position thereof.

2. An element as set forth in claim 1, wherein said yieldably resilientmeans are stressed during said inward movement of said plunger memberand partly relaxed during movement of said plunger member outward ofsaid second chamber when said valve means is in the closed position,said supporting element further comprising limiting means for limitingrelaxation of said yieldably resilient means during said outwardmovement.

3. An element as set forth in claim 1, wherein said yieldably resilientmeans include a sealing member movable relative to said plunger memberand defining therewith a cell, and a body of gas sealed from said secondbody of liquid in said cell by said sealing member.

4. An element as set forth in claim 3, wherein the axially terminalportion of said plunger member in said second chamber is formed with arecess therein, said sealing member being received in said recess formovement inward and outward of said recess, a portion of said recessconstituting said cell and receiving said body of gas.

5. An element as set forth in claim 3, further comprising guide meansaxially guiding said sealing member in said second chamber.

6. An element as set forth in claim 5, wherein said sealing member isformed with a recess therein, the axi-. ally terminal portion of saidplunger member being received in said recess for movement inward andoutward of said recess, a portion of said recess constituting said cell.

7. An element as set forth in claim 5, wherein said guide means includea piston member axially movable in said second chamber and dividing thesame into two compartments, said piston member being formed with athrottling passage connecting said compartments,said plunger memberengaging said piston member.

8. An element as set forth in claim 7, wherein said sealing member isfixedly mounted on said piston member and formed with a recess therein,the axially terminal portion of said plunger member being received insaid recess for movement inward and outward of said recess, a portion ofsaid recess constituting said cell.

9. An element as set forth in claim 3, wherein said partition is formedwith a conduit axially extending thereto, said valve operating meansinclude a rod member elongated in the direction of said axis and havingrespective longitudinal portions outside said cavity, in said firstchamber, and in said conduit, sealing means interposed between said rodmember and said cylinder member permitting axial movement of said rodmember inward and outward of said cavity, said valve means including avalve member mounted on said rod member for movement therewith andsealing said conduit in the closed position of said valve means.

10. An element as set forth in claim 3, wherein said first body ofliquid has a free horizontal surface in said first chamber, said amountof gas making direct contact with said surface.

1. A supporting element of adjustable length comprising, in combination:a. a cylinder member having an axis and defining a sealed cavitytherein; b. a partition fixed to said cylinder member in said cavity andaxially dividing the cavity into a first chamber and a second chamber;c. valve means operatively interposed between said chambers and movablebetween respective open and closed positions in which said valve meansconnects said chambers and seals said chambers from each other; d. valveoperating means accessible outside said cavity for moving said valvemeans between said positions thereof; e. a first body of liquid in saidfirst chamber; f. an amount of a gas under a pressure higher thanatmospheric pressure in pressure-transmitting relationship to said bodyof liquid; g. a plunger member axially movable in said cylindermember,
 1. said plunger member having respective axially terminalportions in said second chamber and outside said cylinder; h. a secondbody of liquid substantially completely filling the remainder of saidsecond chamber and communicating with said first body in said openposition of the valve means,
 1. whereby said gas in the open position ofthe valve means exerts a first axial force on said plunger member in adirection outward of said cavity when said valve means is in the openposition thereof; and i. yieldably resilient means in said secondchamber opposing movement of said plunger member inward of said secondchamber with a second force substantially greater than said first forcewhen said valve means is in the closed position thereof.
 2. An elementas set forth in claim 1, wherein said yieldably resilient means arestressed during said inward movement of said plunger member and partlyrelaxed during movement of said plunger member outward of said secondchamber when said valve means is in the closed position, said supportingelement further comprising limiting means for limiting relaxation ofsaid yieldably resilient means during said outward movement.
 3. Anelement as set forth in claim 1, wherein said yieldably resilient meansinclude a sealing member movable relative to said plunger member anddefining therewith a cell, and a body of gas sealed from said secondbody of liquid in said cell by said sealing member.
 4. An element as setforth in claim 3, wherein the axially terminal portion of said plungermember in said second chamber is formed with a recess therein, saidsealing member being received in said recess for movement inward andoutward of said recess, a portion of said recess constituting said celland receiving said body of gas.
 5. An element as set forth in claim 3,further comprising guide means axially guiding said sealing member insaid second chamber.
 6. An element as set forth in claim 5, wherein saidsealing member is formed with a recess therein, the axially terminalportion of said plunger member being received in said recess formovement inward and outward of said recess, a portion of said recessconstituting said cell.
 7. An element as set forth in claim 5, whereinsaid guide means include a piston member axially movable in said secondchamber and dividing the same into two compartments, said piston memberbeing formed with a throttling passage connecting said compartments,saidplunger member engaging said piston member.
 8. An element as set forthin claim 7, wherein said sealing member is fixedly mounted on saidpiston member and formed with a recess therein, the axially terminalportion of said plunger member being received in said recess formovement inward and outward of said recess, a portion of Said recessconstituting said cell.
 9. An element as set forth in claim 3, whereinsaid partition is formed with a conduit axially extending thereto, saidvalve operating means include a rod member elongated in the direction ofsaid axis and having respective longitudinal portions outside saidcavity, in said first chamber, and in said conduit, sealing meansinterposed between said rod member and said cylinder member permittingaxial movement of said rod member inward and outward of said cavity,said valve means including a valve member mounted on said rod member formovement therewith and sealing said conduit in the closed position ofsaid valve means.
 10. An element as set forth in claim 3, wherein saidfirst body of liquid has a free horizontal surface in said firstchamber, said amount of gas making direct contact with said surface.